Thin-window image pick-up and recording tube

ABSTRACT

A thin-window image pick-up and recording tube comprising an evacuated envelope having a transparent face portion with an elongated thin window, a fluorescent layer being disposed within said window and at least one longitudinal wall of said window being formed to have at least one portion the normal to which is inclined from the normal to said face; deflecting means for deflecting the electron beam emitted from the electron gun to scan said fluorescent layer laterally of said window so that a flying spot is produced in said layer; a plate transparent to said flying spot and disposed on said face so as to cover said window. The thin-window tube is capable of not only recording but picking up optical images with a satisfactory image quality.

O United States Patent 1151 3,676,586 Uno 1451 July 11, 1972 1 THIN-WIN O IMAGE C -U AND 3,341,728 9/1967 Fotland l78/6.7 A RECORDING TUBE 3,470,319 9/1969 McGlamery 1 78/DlG. 2

[72] lnventor: Yoshlhiro Uno, Osaka, Japan Primao, Examiner Roben Richardson [731 Assigneez Ma'sushna Ekctflc Industrial Comp'any- Ass1stantExammerRichard K, Eckert, Jr. Kadoma City, Osaka, Japan Lezdey [22] Filed: July 21, 1970 [57] ABSTRACT [2]] Appl. No.: 56,872 A thin-window image pick-up and recording tube comprising an evacuated envelope having a transparent face portion with an elongated thin window, a fluorescent layer being disposed Foreign Application Priority Data within said window and at least one longitudinal wall of said 59565 window being formed to have at least one portion the normal July 1969 Japan to which is inclined from the normal to said face; deflecting means for deflecting the electron beam emitted from the elec- [52] Cl 178mm 3 tron gun to scan said fluorescent layer laterally of said window 04 3 16 so that a flying spot is produced in said layer; a plate trans- [Sl] Ill. Cl. ll parent to said y g p and disposed on said face so as to [58] Field Of Search l 78/6.7 R, 6.7 A, DIG. 28, cover Said window. The thinwvindow tube i capable of not 178/72; 313/891 92 92 F1 1 13 only recording butpicking up optical images with a satisfactory image quality. [56] References Cited UNITED STATES PATENTS 15 Claims, 13 Drawing Figures 3,225,137 l2/l965 Johnson ..l78/6.7 A

22 z z swei fezf flc/ P'A'TE'NTEDJUL 1 1 m2 SHEET k [If 4 INVENTOR YOSHIHIRO UNO ATTOR Y THIN-WINDOW IMAGE PICK-UP AND RECORDING TUBE This invention relates to a thin-window cathode-ray tube of the character in which a light beam modulated by an object bearing images thereon is reflected from a reflector to be oriented in a direction substantially perpendicular to the center line of an elongated window and is transferred to lightsensitive means positioned outside of the envelope of the tube, whereby optical images are not only recorded in a usual manner but picked up in a novel manner with use of a single unit.

A variety of cathode-ray tubes for recording purposes have heretofore been developed, in which an electron beam is converted into a light beam with use of phosphors. The resultant light beam is caused to act upon a recording medium without resorting to the use of a lens or other optical system. A fiberoptics cathode-ray tube and a thin-window cathode-ray tube are two of the representative devices used advantageously for putting such a scheme into practice. Regarding the cathoderay tube of fiber-optics type, attempts have been made so as to make it possible to record and pick up optical images in one and the same unit tube.

A practice taken up in the fiber-optics tube is proposed to have a translucent reflector or a half mirror interposed between the ends of the fiber-optics element. In this instance, the light, which is emitted from phosphors irradiated by an electron beam, passes through the translucent reflector and transferred to an object carrying optical images thereon. Then, the light modulated by the object returns again into the fiber-optics element. The light having once passed through the element is, for a second time, oriented perpendicularly by the translucent reflector, and is thereafter guided to light-sensitive means. Another representative practice is to guide to the lightsensitive means a portion of the light that leaks from the vicinity of the junction of the fiber-optics element with the object bearing images thereon.

Problems are, however, experienced in these known practices in that the fiber-optics element, which of itself is complex in construction, becomes further complicated as a result of the provision of the image pick-up mechanism. This results in an appreciable reduction in signal-to-noise ratio (S/N ratio) of the image transferred therethrough. Moreover, the fiber-optics element is extremely costly and requires highly developed techniques for production.

It is, therefore, an object of this invention to provide a novel thin-window image pick-up and recording tube, in which a light beam modulated by an object bearing images thereon is reflected from a reflector to be oriented in a direction substantially perpendicular to the center line of an elongated thin window and is transferred to light-sensitive means positioned outside of the envelope of the tube.

Another object of the invention is to provide a novel thinwindow image pick-up and recording tube of a type which is easy and economical to manufacture and simple in construction and which is capable of not only recording but picking up optical images with a satisfactory image quality.

Still another object is to provide a novel thin-window cathode-ray tube adapted to record and pick-up an optical image, comprising an evacuated envelope having a transparent face portion with an elongated thin window, a fluorescent layer being disposed within said window and at least one longitudinal wall of said window being formed to have at least one portion the normal to which is inclined from the normal to said face; deflecting means for deflecting the electron beam emitted from the electron gun to scan said fluorescent layer laterally of said window so that a flying spot is produced in said layer; a plate transparent to said flying spot and disposed on said face so as to cover said window.

The invention will be described in more detail with reference to the accompanying drawings in which:

FIG. 1 is a schematic view showing the overall construction of a preferred embodiment of the recording tube tin-window cathode-ray tube of the invention;

FIG. 2 is a schematic illustration of the principle of the recording operation of the thin-window cathode-ray tube of the invention;

FIG. 3 is a schematic illustration of the principle of the image pick-up operation of the thin-window cathode-ray tube of the invention;

FIG. 4 is a lengthwise section of the elongated thin window showing, on an enlarged scale, a part of the cathode-ray tube according to the invention;

FIGS. 5a to 5d are explanatory illustrations showing the image pick-up operations of the elongated thin window having walls with modified shapes, wherein FIG. 5a is an example in which the wall has a uniplanar tapered surface, FIG. 5b is an example in which the wall has biplanar tapered surfaces, FIG. 50 is an example in which the wall has a parabolic surface, and FIG. 5d is an example in which the wall has an elliptical surface;

FIGS. 61: to 6d are illustrations showing arrangements which are used for detecting the light beam reflected by the wall of the window, wherein FIG. 6a is an example in which a photosensitive material is applied to the side end wall of the face portion of an evacuated envelop, FIG. 6b is an example, shown in a lengthwise section, of an arrangement using a pair of lenses and photo-multipliers, FIG. 6c is an example, shown in a bottom end view, of another arrangement using a pair of Fresnel lenses and photo-multipliers and FIG. 6d is an example in which a combined lens and two photo-multipliers are provided on each side of the face portion of the evacuated tube so as to be operable to pick up images on an object of an elongated width; and

FIG. 7 is a block diagram of a preferred example of an electric arrangement which is adapted for use with the thin-window cathode-ray tube according to the invention.

Referring first to FIG. 1, the thin-window cathode-ray tube of the invention, which is designated generally by numeral 10, comprises an evacuated envelope 11, an electron gun 12, an elongated thin window assembly 13, a base 14, focussing means 15, and deflecting means 16. Designated by numeral 17 is a path of an electron beam emitted from the electron gun 12.

The electron beam 17 emitted from the electron gun 12 is focussed and deflected by the focussing and deflector means 15 and 16, respectively, into a sufficient minute spot beam, as the beam approaches and scans an elongated window 13 unidirectionally. The electron beam, which has bombarded the window 13, causes a fluorescent layer, for instance, phosphors applied to the window 13 to luminesce. The light thus evolved then irradiates an object or a sensitized sheet (not shown) which is positioned in close contact with the foremost end of the window 13.

FIG. 2 illustrates, in a lengthwise sectionof the window 13 on an enlarged scale, a part of the thin-window cathode-ray tube shown in FIG. 1. As shown, the electron beam 17 that is rendered into a flux of diameter d irradiates a fluorescent layer 19 which is applied to the inner surface of a plate 18 made of a suitable transparent material such as glass or mica, so that the fluorescent layer 19 is caused to luminesce. Light rays, thus emitted from the fluorescent layer and indicated by numeral 20 advance through the plate 18 as indicated by arrows in solid lines. If, in this instance, the angle (the incident angle) (a) of the direction of the light rays 20 from the line perpendicular to the surface of the plate 18 is small, then the light rays 20 pass through the plate 18 and irradiate an object or a sensitized sheet 21 with an intensity corresponding to that of the initial electron beam 17.

Let n be the index of refraction of the material of the plate 18 with respect to air or vacuum. If, now, the value a, (critical angle) which is derived from the equation:

sin a l/n exceeds the above mentioned incident angle (1,, then the light rays 20 are totally reflected from the surface (the outer surface being exposed to the open air) of the plate 18, which is held in contact with the sensitized sheet 21, and are prevented from reaching the sheet 21. It therefore follows that only that portion of the rays which are indicated by diameter D in FIG. 2 is allowed to reach the sheet 21. If, here, the thickness of the plate 18 be t, then:

D=d+2rtana 2 as will be understood from FIG. 2. Thus, the value D is determined exclusively by the values d and t and the value a which is inherent in the material forming the plate 18.

It will now be understood from the foregoing analysis that, although the light rays 20 are diffused rays in common thinwindow tubes, the deterioration in the resolution of the images recorded on the sensitized sheet 21 is limited within a certain range. Furthermore, experiments have revealed that the coefficient of the optical contact of the fluorescent layer 19 with the inner surface of the plate 18 is smaller than about 0.1, implying that the fluorescent layer 19 is optically in little contact with the plate 18. This further means that the light rays 20 advance from an optically less dense environment (vacuum or air) into a dense material (which may be glass, for instance) and that the light rays 20 are not totally reflected either from the inner surface of the plate 18. Since, therefore, a major portion of the light rays within the range of D are permitted to reach the sensitized sheet 21, the input light can be utilized with increased efficiency as compared with the existing tubes where a lens or the like is used.

The present invention thus contemplates improvement of the thin-window cathode ray tube which, as previously noted, features a high resolution power and excellent efficiency of light transfer, so that the cathode-ray tube can be used not only for recording but for image pick-up purposes; the thinwindow cathode-ray according to the invention, more specifically, will provide an increased S/N ratio because that an unnecessary portion of the light is totally reflected and prevented from passing to the sensitized sheet.

FIG. 3 is now presented for the purpose of discussing the principle of image pick-up operation of the thin-window cathode-ray tube according to the invention, showing, in a section on an enlarged scale, the plate 18 and an object or a copy of manuscript bearing images thereon. In FIG. 3, the reference numeral '22 designates, in lieu of the sensitized sheet 21 of FIG. 2, an object or a copy of manuscript bearing optical images thereon. An area 22a of the copy 22 corresponds to that area D of the sensitized sheet to which the light rays 20 irradiate as illustrated in FIG. 2. The area 22a of the copy can, therefore, be considered to be a source of diffused light.

More specifically, an electron beam of a certain intensity irradiates the area 22a during image pick-up operation so that light rays 23 emanating from the source or the area 22a of diffused light are endowed with an intensity that is dictated by the thickness, or the blackness, of the patterns of the images on the area 22a. Thus, it will be understood that only that portion of the light rays 23 from the area 22a which is represented by the reference character H in FIG. 3 can be admitted through the plate 18, as is apparent from the previous discussion with reference to FIG. 2.

Because the copy 22 and the plate 18 may be isolated from each other, the light rays 23 reflected from and modulated in intensity by the area 22a are not totally reflected.

If, therefore, a suitable photo-sensitive element (not shown) is provided within the range H, the images on the area. 22a could be picked up simply by detecting the rays 23 from a purely theoretical point of view. The range H is, however, so small that it is practically impossible to have the fluorescent layer 19 and the photoelectric element accommodated in that particular range. The range H is mathematically expressed as:

H=d+4t-tana (3) similarly to the range D of the equation (2). If, in this instance, the variables d, t and a, are substituted by d 100 u, t= 100 and a =40 (as in the case of the plate made of glass), then H is as small as 400 u.

According to this invention, therefore, that portion of the light rays 23 which has returned into the range H is reflected by the wall of the window 13 and oriented to a direction substantially perpendicular to the direction of the initially emitted electron beam. The thus oriented light is transferred to lightsensitive means positioned outside of the envelope of the tube for conversion of optical signals into electric signals, whereby the difficulties encountered in the conventional thin-window tubes can be eliminated.

FIG. 4 is an enlarged sectional view of a part of a preferred embodiment of the thin-window cathode-ray tube implementing this invention. Designated by reference numeral 24 in FIG. 4 is a metal backing made of a metal such as Al, Au or Ni which is deposited through vacuum evaporation on the inner surface of the evacuated envelope 11. The metal backing 24, which has a reflective surface, serves for the purpose that the light emanating from the fluorescent layer 19 as a result of the irradiation of the electron beams is prevented from being transferred to the light-sensitive means without being modulated by the images on the copy 22 and thus from reducing the S/N ratio. The metal backing 24 also serves for the purpose that, in case excess phosphors are deposited on a portion or portions of the inner surface of the envelope 11 in the course of projection of the thin-window cathode-ray tube 10, the light rays emitted from such unduly formed fluorescent layer 19 are intercepted. It may be mentioned that, if desired, the effect of reflection may be attained otherwise, say, by utilizing the total reflection at the wall of the window 13 or by the formation of a dielectric film. Designated by reference numeral 25 is another metal backing usually mounted also on a conventional cathode-ray tube, whereby an electron beam passes therethrough but the light rays 20 of FIG. 2 are prevented from entering the envelope 11. The reflective surface 24 is herein shown as slanting at an angle 0 from the direction perpendicular to the surface of the plate 18, which angle 0 is determined in such a manner that the light 23 is oriented in a direction substantially perpendicular to the direction of the center line of the elongated thin window and in which the electron beam is initially emitted (preferably at 45). The evacuated envelope 11 and the plate 18 may be optically not held in contact with each other, as seen from a clearance 26 separating the two elements 1 1 and 18 so that the light which has been totally reflected from the outer or copy side surface of the plate 18 due to the little optical contact between the fluorescent layer 19 and the plate 18 is, if any, further totally reflected on the inner surface ofthe plate 18, whereby the S/N ratio can be improved. However the clearance 26 between the plate 18 and the fluorescent layer 19 may be filled with glass or a suitable adhesive flller.

This will be explained by the fact that the fluorescent layer 19 and the plate 18 are only 10 percent in optical contact with each other as previously noted and that only a minor portion of the light is totally reflected at the outer surface of the plate 18 and is returned inwardly of the tube.

The principle of image pick-up operation of the thin-window cathode-ray tube according to the invention will now be discussed with reference to FIG. 4. As previously noted, the electron beam irradiates with a substantially constant intensity during image pick-up operation so that the light detected at the side end of the face portion of the evacuated envelope l1 accounts mostly for the light rays 23, the intensity of which has been modulated in intensity by the images on the area 22a. The light rays 23, which advance upwardly of FIG. 4 at an incident angle that is smaller than a will pass through the clearance 26 and enter the envelope 1 1. Therefore, the loss of the light rays 23 caused by the total reflection at the inner surface of the plate 18 is practically negligible with the plate 18 and the evacuated envelope 11 kept optically isolated from each other. The resultant light rays 23 are now reflected by the metal backing 24 deposited on the wall of the window 13 and are caused to advance in the lateral direction of FIG. 4. If, therefore, one or a plurality of suitable light-sensitive means is positioned in the lateral direction the light rays advancing in this direction can be detected, in which instance the light-sensitive means may be easily manipulated from the outside of the evacuated envelope 11, if desired.

It will now be appreciated from the foregoing detailed description, the thin-window cathode-ray tube according to the invention features freedom from irregular configurations of the fiber optics elements and surface noises, a satisfactory S/N ratio which is fully acceptable for all practical purposes, and an increased efficiency with which the luminescent light is utilized.

FIGS. 5a to 5d illustrate examples of the wall of the window 13 of the thin-window cathode-ray tube 10 according to this invention. The wall shown in FIG. 5a is formed in such a manner that a portion of the metal backing or reflective surface 24 is uniplanarly tapered. The slit portion of the reflective surface 24 may also be slightly tapered so as to pass the major portion of the electron beam through the elongated thin window even though the slit portion of the window 13 is rather roughly wrought out. This is because the width of the window 13 is as small as 100 t, often intercepting a substantial portion of the incoming electron beam. The thickness t (for instance 100 p.) of the plate 18 is so small as compared with the thickness (for instance 10 mm) of the wall of the envelope 11 that the afore-mentioned light rays 23 can be assumed to emanate approximately from a light source in FIG. a. The light rays are thus considered to advance in the direction of the arrows as is the case with a usual reflector, if it is assumed that an imaginary source 0 of light lies as illustrated.

FIG. 5b shows another shape wall having biplanarly tapered reflective surfaces, wherein a portion of the reflective surface is dual-tapered at suitable angles in view of the fact that the light rays emanating from the point 0 are distributed in a smaller quantity as the incident angle thereof becomes greater. The function of the wall shown here is essentially similar to that which has been discussed in connection with the example of FIG. 5a and, as such, the repeated discussion thereof is herein omitted.

FIG. 50 illustrates still another wall having a parabolic reflective surface, wherein the focus F of the parabolic surface 24 is situated in such a manner that the light rays advancing in the lateral direction can be focussed. In FIG. 5d, the reflective surface 24 is configured as elliptical so that, if the focus F is pertinently situated, the same result as attained in the reflective surface of FIG. 5c can be obtained.

The wall usable in the thin-window cathode-ray tube according to the invention is not limited to those cases which have been shown and described but includes any modification insofar as the light rays 23 can be efficiently oriented in a direction perpendicular to the direction of the electron beam.

FIGS. 6a to 6d illustrates examples of the method of detecting the guided light rays. In FIG. 6a, a photo-conductive material 27 acting as light-detecting means is applied to the outer side face of the envelope 11, whereby the light rays which have been modulated in intensity is converted into electric signals. In this instance, the photo-conductive material 27 may be applied either direct to the envelope II or through a third layer (not shown) coated on its outer surface with the photo-conductive material so that the third layer can be removed complete with the photo-conductive layer from the envelope for the purpose of repair.

FIGS. 6b and 60 show other examples of the method of detecting the reflected light rays through convex lenses, by which the light rays are focussed while they are being reflected, the former being a sectional view and the latter being a bottom end view of the window 13 of FIG. 6b. As shown, the light-detecting means may include a pair of lenses 28 and a pair of photomultipliers 29. The lenses 28 may be preferably of Fresnel type which is adapted to have available an increased focussing efficiency, in view of the fact that the slit portion of the window 13 is, for instance, about cm long, as seen in FIG. 60. Since, moreover, a pair of photomultipliers 29 are positioned on both sides of the face portion of the envelope 11, the electron beam can be controlled in a manner to be in alignment with the center line of the window 13, as will be discussed in detail with reference to FIG. 7.

The evacuated envelope I] and the plate 18 of FIG. 6b can be assembled in a manner described in the following. As previously mentioned, it is important that the envelope 11 and the plate 18 be hermetically sealed off. In order practically to meet the requirement, a spacer which is, for instance, u thick may be inserted into the window assembly 13 so as to fixedly maintain the width of the window 13 and an adhesive frit glass 30 may be fastened to the peripheral edge of the end surface of the evacuated envelope 11, which peripheral edge may have been indented at a suitable angle as illustrated in FIG. 6b or stepped up. The plate 18 is then applied under pressure to the frit glass.

Practically no difficulty is encountered in the forming the window 13 to the envelope in this manner, enabling the production of the thin-window cathode-ray tubes with improved efficiency.

FIG. 6d illustrates a method of separately focussing the reflected light rays with use of a combined Fresnel lens 28 and two photomultipliers 29 which are positioned on each side of the face portion the envelope 11, which method is adapted particularly where an evacuated envelope having an unusually elongated thin window is to be used.

FIG. 7 is a block diagram showing a preferred electric arrangement 30 adapted for use with a facsimile apparatus using the thin-window cathode-ray tube 10 embodying the invention. The arrangement 30 includes a reception unit, transmission unit and balancer unit which serves to automatically regulate the precise position of the electron beam perpendicularly of the scanning path. As illustrated, the electric arrangement 30 comprises as customary an image amplifier 32, an amplifier 33 for the deflector coil, an amplifier 34 for the focussing coil, a detector unit 35, a receiver amplifier 36, amplifiers 37 and 38 for amplifying the input signals supplied from the light-detecting means, for example, a pair of the two photomultipliers, a comparator unit 39, a transmitter amplifier 40, a mixer unit 41, a synchronizer unit 42, and a modulator unit 43. The amplifiers 37 and 38 and the comparator unit 39 constitute the balancer unit in cooperation with the two light-detecting means. On the other hand, the reception unit is composed of the video image amplifier 32, deflection amplifier 33, detector unit 35 and receiver amplifier 36, while the transmission amplifier is composed of the transmittor amplifier 40, mixer unit 41, synchronizer unit 42 and modulator unit 43.

The circuit arrangement 30 shown in FIG. 7 operates in a manner described as follows:

When in receiving the electric signals for recording purposes, the receiver amplifier 36 amplifies the received signals of varying intensity and the signals thus amplified are then applied to the video image amplifier 32 via the detector unit 35. The output signals from the image amplifier 32 control the intensity of the electron beam which is emitted from the electron gun 12. The electron beam is converged by the focussing means 15 into a sufficiently small spot beam, which is thereafter deflected by the deflector means 16 and scans the window 13. This scanning signal is fed to the amplifier 33 by the detector unit 35 in synchronism with the signal fed from the detector unit 35.

When, on the other hand, in the transmission of image signals for image pick-up purposes, an electron beam which is regulated to a constant intensity by the image amplifier 32 is emitted from the electron gun 12. In this instance the light which is reflected from an object bearing thereon optical images and which is modulated in intensity by the thickness or blackness of the images is introduced into the photomultipliers 29 or other similar light-sensitive means. The electric signals supplied from the photomultipliers are then passed through the amplifiers 37 and 38 for amplification. The outputs of these amplifiers are transferred through the comparator unit 39 to the transmitter amplifier 40. Although two lightsensitive, means are illustrated as used in the circuit, such means may be only one in number, in which instance the position of the electron beam can not be controlled automatically. The electric signals amplified by the transmitter amplifier 40 are then fed to the mixer unit 41, where the signals are mixed with or superposed on those applied from the synchronizer unit 42 and the resultant superposed signals are converted into a transmitting wave by the modulator unit 43.

The operation of the balancer unit is such that, both for the image recording and pick-up purposes, the comparator unit 39 acts to compare the signal voltages supplied from the amplifiers 37 and 38 to which are introduced the electric signals from the photomultipliers 29 and to feed back the voltage difference to the deflector means 16 through the deflector amplifier 33, whereby the electron beam is automatically controlled to scan exactly the center line of the window 13.

it should now be appreciated that the thin-window cathoderay tube according to the invention is advantageous for practical purposes because of its simplified construction, satisfactory S/N ratio, improved resolution, and increased percentage of the light utilized.

What is claimed is:

1. A thin-window cathode'ray tube adapted to record and pick up an optical image, which comprises:

an evacuated envelope having a transparent face portion with a elongated thin window, a fluorescent layer being disposed within said window, said window having two longitudinal walls at least one of which being formed to have at least one portion the normal to which is inclined from the normal to said face;

deflecting means for deflecting the electron beam emitted from the electron gun to scan said fluorescent layer laterally of said window so that a flying spot is produced in said layer;

light-detecting means disposed sidewardly of said transparent face portion, and

a plate transparent to the light and disposed on said face to cover said window.

2. A thin-window cathode-ray tube according to claim 1, wherein each longitudinal wall of said window is formed so as to have at least one portion the normal to which is inclined from the normal to said face.

3. A thin-window cathode-ray tube according to claim 1, wherein said face and said plate are kept isolated from each other.

4. A thin-window cathode-ray tube according to claim 3, further comprising a frit glam interposed between said thin window and the peripheral edge of the foremost end of said envelope, which edge has been previously indented at a suitable angle.

5. A thin-window cathode-ray tube according to claim 1, wherein a light-reflective surface of a metal backing is applied to said wall.

6. A thin-window cathode-ray tube according to claim 5, wherein said wall is uniplanarly tapered. I

7. A thin-window cathode-ray tube according to claim 5, wherein said wall is biplanarly tapered.

8. A thin-window cathode-ray tube according to claim 5, wherein said wall is configured as parabolic and the focus of the parabolic surface is situated in such a manner that the reflected light can be focused while advancing perpendicularly of the scanning direction of the electron beam.

9. A thin-window cathode-ray tube according to claim 5, wherein said wall is configured as elliptical and the emitted light can be focussed while advancing perpendicularly of the scanning direction of the electron beam.

10. A thin-window cathode-ray tube according to claim 1, wherein said light-detecting means comprises a photoconductive layer applied to the outer side surface of said envelope, whereby the light is converted into electric signals.

11. A thin-window cathode-ray tube according to claim 10, wherein said photoconductive layer is applied direct to said envelope.

12. A thin-window cathode-ray tube according to claim 10, wherein said photoconductive layer is applied through an other layer coated on said envelope with said photoconductive layer, whereby the second named layer can be removed complete with said photoconductive layer from said envelope for gurxose of repair.

1 thin-window cathode-ray tube according to claim 1,

wherein said light-detecting means comprises a convex lens and a photomultiplier on the side of said envelope.

14. A thin-window cathode-ray tube according to claim 13, wherein said convex lens is of Fresnel type which is adapted to have available an increased focussing efficiency. comparator 15. A facsimile apparatus comprising in combination a thinwindow cathode-ray tube, including an evacuated envelope having a transparent face portion with an elongated thin window, a fluorescent layer being disposed within said window and at least one longitudinal wall of said window being formed to have at least one portion the normal to which is inclined from the normal to said face;

deflecting means for deflecting the electron beam emitted from the electron gun to scan said fluorescent layer laterally of said window so that a flying spot is produced in said layer;

a plate transparent to said flying spot and disposed on said face so as to cover said window; and an electrical arrangement including reception, balancer and transmission units, wherein said reception unit has a receiver amplifier for amplifying the received electric signals, a detector unit for detecting the electric signals applied thereto from said receiver amplifier, a video image amplifier for amplifying the detected signals and applying them to said electron gun, and a deflection amplifier for amplifying the detected signals and applying them to said deflector means; said balancer unit has a pair of amplifiers connected respectively to a pair of said light-detecting means for amplifying the applied electric signals independently of each other, and a comparator unit for comparing the signal voltages applied thereto from a pair of the last named amplifiers and for feeding back the voltage difference to said deflector amplifier; and said transmission unit has a transmitter amplifier for amplifying the electric signal applied thereto from said comparator unit, a synchronizer unit for generating a synchronized electric signal, a mixer unit for mixing the electric signal applied from said transmitter amplifier with the electric signal applied from said synchronizer unit, and a modulator unit for converting the mixed electric signal into a transmitting wave; whereby the electron beam is automatically controlled to precisely scan the center line of said window of said thinwindow cathode-ray tube. 

1. A thin-window cathode-ray tube adapted to record and pick up an optical image, which comprises: an evacuated envelope having a transparent face portion with a elongated thin window, a fluorescent layer being disposed within said window, said window having two longitudinal walls at least one of which being formed to have at least one portion the normal to which is inclined from the normal to said face; deflecting means for deflecting the electron beam emitted from the electron gun to scan said fluorescent layer laterally of said window so that a flying spot is produced in said layer; light-detecting means disposed sidewardly of said transparent face portion, and a plate transparent to the light and disposed on said face to cover said window.
 2. A thin-window cathode-ray tube according to claim 1, wherein each longitudinal wall of said window is formed so as to have at least one portion the normal to which is inclined from the normal to said face.
 3. A thin-window cathode-ray tube according to claim 1, wherein said face and said plate are kept isolated from each other.
 4. A thin-window cathode-ray tube according to claim 3, further comprising a frit glass interposed between said thin window and the peripheral edge of the foremost end of said envelope, which edge has been previously indented at a suitable angle.
 5. A thin-window cathode-ray tube according to claim 1, wherein a light-reflective surface of a metal backing is applied to said wall.
 6. A thin-window cathode-ray tube according to claim 5, wherein said wall is uniplanarly tapered.
 7. A thin-window cathode-ray tube according to claim 5, wherein said wall is biplanarly tapered.
 8. A thin-window cathode-ray tube according to claim 5, wherein said wall is configured as parabolic and the focus of the parabolic surface is situated in such a manner that the reflected light can be focused while advancing perpendicularly of the scanning direction of the electron beam.
 9. A thin-window cathode-ray tube according to claim 5, wherein said wall is configured as elliptical and the emitted light can be focussed while advancing perpendicularly of the scanning direction of the electron beam.
 10. A thin-window cathode-ray tube according to claim 1, wherein said light-detecting means comprises a photoconductive layer applied to the outer side surface of said envelope, whereby the light is converted into electric signals.
 11. A thin-window cathode-ray tube according to claim 10, wherein said photoconductive layer is applied direct to said envelope.
 12. A thin-window cathode-ray tube according to claim 10, wherein said photoconductive layer is applied through an other layer coated on said envelope with said photoconductive layer, whereby the second named layer can be removed complete with said photoconductive layer from said envelope for purpose of repair.
 13. A thin-window cathode-ray tube according to claim 1, wherein said light-detecting means comprises a convex lens and a photomultiplier on the side of said envelope.
 14. A thin-window cathode-ray tube according to claim 13, wherein said convex lens is of Fresnel type which is adapted to have available an increased focussing efficiency. comparator
 15. A facsimile apparatus comprising in combination a thin-window cathode-ray tube, including an evacuated envelope having a transparent face portion with an elongated thin window, a fluorescent layer being disposed within said window and at least one longitudinal wall of said window being formed to have at least one portion the normal to which is inclined from the normal to saiD face; deflecting means for deflecting the electron beam emitted from the electron gun to scan said fluorescent layer laterally of said window so that a flying spot is produced in said layer; a plate transparent to said flying spot and disposed on said face so as to cover said window; and an electrical arrangement including reception, balancer and transmission units, wherein said reception unit has a receiver amplifier for amplifying the received electric signals, a detector unit for detecting the electric signals applied thereto from said receiver amplifier, a video image amplifier for amplifying the detected signals and applying them to said electron gun, and a deflection amplifier for amplifying the detected signals and applying them to said deflector means; said balancer unit has a pair of amplifiers connected respectively to a pair of said light-detecting means for amplifying the applied electric signals independently of each other, and a comparator unit for comparing the signal voltages applied thereto from a pair of the last named amplifiers and for feeding back the voltage difference to said deflector amplifier; and said transmission unit has a transmitter amplifier for amplifying the electric signal applied thereto from said comparator unit, a synchronizer unit for generating a synchronized electric signal, a mixer unit for mixing the electric signal applied from said transmitter amplifier with the electric signal applied from said synchronizer unit, and a modulator unit for converting the mixed electric signal into a transmitting wave; whereby the electron beam is automatically controlled to precisely scan the center line of said window of said thin-window cathode-ray tube. 